NCI is using a stepwise approach to assess the potential of various agents to inhibit, reverse and/or delay the carcinogenic process in various organs. One of the preclinical evaluations of potential chemopreventive agents is the demonstration of agent efficacy in preventing cancer in laboratory animal models. Both carcinogen-induced and transgenic animals are used for this purpose. Another area of preclinical development in chemopreventive agents is the development of surrogate intermediate endpoint biomarkers. Such biomarkers must be translatable to the clinic trial situation in order to shorten the time required to evaluate agents clinically in Phase II trials.